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Research Papers

Abdominal Aortic Aneurysm Risk of Rupture: Patient-Specific FSI Simulations Using Anisotropic Model

[+] Author and Article Information
Peter Rissland, Yared Alemu, Shmuel Einav

Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY 11794-8181

John Ricotta

Department of Surgery, Stony Brook University Hospital, 101 Nicolls Road, Stony Brook, NY 11794-8191

Danny Bluestein1

Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY 11794-8181danny.bluestein@sunysb.edu

1

Corresponding author.

J Biomech Eng 131(3), 031001 (Dec 31, 2008) (10 pages) doi:10.1115/1.3005200 History: Received January 07, 2008; Revised June 18, 2008; Published December 31, 2008

Abdominal aortic aneurysm (AAA) rupture represents a major cardiovascular risk, combining complex vascular mechanisms weakening the abdominal artery wall coupled with hemodynamic forces exerted on the arterial wall. At present, a reliable method to predict AAA rupture is not available. Recent studies have introduced fluid structure interaction (FSI) simulations using isotropic wall properties to map regions of stress concentrations developing in the aneurismal wall as a much better alternative to the current clinical criterion, which is based on the AAA diameter alone. A new anisotropic material model of AAA that closely matches observed biomechanical AAA material properties was applied to FSI simulations of patient-specific AAA geometries in order to develop a more reliable predictor for its risk of rupture. Each patient-specific geometry was studied with and without an intraluminal thrombus (ILT) using two material models—the more commonly used isotropic material model and an anisotropic material model—to delineate the ILT contribution and the dependence of stress distribution developing within the aneurismal wall on the material model employed. Our results clearly indicate larger stress values for the anisotropic material model and a broader range of stress values as compared to the isotropic material, indicating that the latter may underestimate the risk of rupture. While the locations of high and low stresses are consistent in both material models, the differences between the anisotropic and isotropic models become pronounced at large values of strain—a range that becomes critical when the AAA risk of rupture is imminent. As the anisotropic model more closely matches the biomechanical behavior of the AAA wall and resolves directional strength ambiguities, we conclude that it offers a more reliable predictor of AAA risk of rupture.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

(a) and (c) show the MMS depiction of patient A and B AAA geometries as obtained from CT scans, respectively. (b) and (d) depict the resulting reconstructed mesh geometries, respectively. The geometries are cross sectioned to expose the ILT region and the AAA wall and lumen.

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Figure 2

Stress-strain relationship of the simulated biaxial testing using the orthotropic material model as compared to the experimental results from Ref. 21

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Figure 3

Velocity (a) and pressure (b) waveforms imposed at the inlet and outlet (reproduced from Ref. 29). Inlet peak systolic flow occurs at 0.25s and peak systolic pressure occurs at 0.32s.

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Figure 4

Differences in wall motion between the two material models employed

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Figure 5

Patient A and patient B velocity vectors flow fields (coronal cross-sectional view)

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Figure 6

Patient A wall von Mises stresses at peak systolic pressure for the isotropic model with ILT

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Figure 7

Patient A wall von Mises stresses at peak systolic pressure for the anisotropic model with ILT

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Figure 8

Patient A wall von Mises stresses at peak systolic pressure for the isotropic model without ILT

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Figure 9

Patient A wall von Mises stresses at peak systolic pressure for the anisotropic model without ILT

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Figure 10

Maximum and averaged von Mises over the entire wall for patient A: (a) with ILT and (b) without ILT. Lines represent the anisotropic model and isotropic model (according to the legend).

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Figure 11

Patient B von Mises stress at the outer wall for the isotropic material with ILT at peak systolic pressure

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Figure 12

Patient B von Mises stress at the outer wall for the anisotropic material with ILT at peak systolic pressure

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Figure 15

Maximum and averaged von Mises stress over the entire wall for patient B: (a) with ILT (b) without ILT. Lines represent the anisotropic model and the isotropic model (according to the legend).

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Figure 14

Patient B von Mises stress at the outer wall for the anisotropic material without ILT at peak systolic pressure

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Figure 13

Patient B von Mises stress at the outer wall for the isotropic material without ILT at peak systolic pressure

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